1. Field of the Invention
The present invention relates to a wire electrical discharge machine and an electrical discharge method using the wire electrical discharge machine. More particularly, the present invention relates to a wire electrical discharge machine and a wire electrical discharge method for reducing machining damage during cutting machining and escape machining.
2. Description of the Related Art
When performing an electro-discharging machining on a workpiece using a wire electrical discharge machine, it is important to improve machining accuracy of a shape, including an approach portion which corresponds to an end of a section (approach section) where the wire electrode approaches for performing cutting machining on the workpiece. Shapes machined by the wire electro-discharging machining include a punch shape and a die shape, and when these shapes are machined, machining damage as streaks may be caused due to the discharge to the approach portion of the workpiece. This is a phenomenon that occurs as follows. Discharge starts several micrometers before a final arrival position of a position of a command (a command by a move block of the approach portion) for moving the wire electrode of the wire electrical discharge machine, and electro-discharging machining is performed more than necessary before reaching the final position. As a result, machining damage as streaks is caused in the approach portion.
Further, when the wire electrode comes closer to the workpiece machining surface during cutting machining (during approach) and when the wire electrode moves away from the workpiece machining surface during escape machining (during escape process), the approach portion is machined twice (double machining), and this makes such machining damage more conspicuous. Therefore, as the number of cutting processing increases, the machining damage becomes more conspicuous.
In the past, a technique for suppressing the machining damage as streaks has been suggested.
Japanese Patent Application Laid-Open No. 2004-276127 discloses a wire electrical discharge method for generating a program which executes machining of a machining path along a die shape multiple times by changing the cutting position in each machining process. This method is a method for generating a program which executes machining of a machining path along a die shape multiple times by changing the cutting position in each machining, and it takes time to regenerate the program, and this method may sometimes be inapplicable to machining of such a complicated shape as a plurality of approach paths could not be provided thereon.
Japanese Patent Application Laid-Open No. 6-143037 discloses a technique for starting cutting process while inclining a wire electrode in a machining direction and maintaining a predetermined angle with respect to a workpiece, and when the cutting process is carried out for a predetermined distance from the cutting start, an inclination angle of the wire electrode is gradually changed to a specified inclination angle of the machining program, and further, electro-discharging machining is performed along a planned shape. This method is a technique for inclining the wire electrode in a machining direction in order to suppress vibration that occurs in the wire electrode during cutting, and is unable to reduce machining damage during cutting machining and escape machining.
WO 2003/045614 discloses a method for increasing or reducing the machining energy, and generating a shape in proximity to an approach point on a machining surface of a workpiece into a protruding shape or recessed shape in accordance with the purpose of the workpiece with a desired degree. However, this electrical discharge method is to adjust the shape in proximity to an approach point on the machining surface of the workpiece into a desired shape in accordance with the purpose, which does not suppress machining damage in proximity to the approach point.
Japanese Patent Application Laid-Open No. 2011-83866 discloses a technique for performing control for preventing excessive discharge by adjusting machining energy used during escape machining and approach machining during die machining, and suppressing machining damage of a workpiece.